1. Field of the Invention
The invention relates to a pressure or pressure medium cylinder with a terminally closed, tubular casing having a sealed elongated slot and in whose cylindrical interior is guided in longitudinally displaceable manner a sealed piston, which has a lateral force reducing projection extending through the elongated slot. Pressure cylinders of this type, which are also known as piston rod-free pressure cylinders, have the advantage of limited space requirements.
2. Prior Art
A pressure cylinder of this type is already known (EP-Al-190 760), which has a locking brake, The latter contains two brake elements, which act on the casing in the vicinity of the elongated slot, namely in the axial ends of the working piston. In this way the length of the force reducing projection is greater than the length of the working piston, so that there is an overall reduction in the movement range of the pressure cylinder.
A further working cylinder of this type is known (DE-Al-33 28 292), in which a brake profile is arranged laterally alongside the cylinder casing and is fixed at both ends to the two cylinder heads. The braking mechanism is connected by means of a U-shaped member to the force reducer. Apart from the additional lateral space requirement, this results in that forces occurring on braking are asymmetrically transferred to the force reducer and therefore to the piston.
In the case of piston rod-free working cylinders not having an elongated slot, but which operate with the aid of a seal strip which longitudinally traverses the cylinder, it is known (DE-Ul-79 31 576), to displace a slide on the outside of the cylinder casing and which operates in the opposite direction to the working piston. This slide can concentrically embrace the cylinder tube with a brake lining and press the same inwards. However, this construction suffers from the disadvantage that the outside of the casing is no longer available for other components, e.g. positioning switches, scales provided with locking means, etc.
It is also known in connection with piston rod-free working cylinders (DE-OS No. 24 53 948) to provide brake wedges or chocks in the cylinder working bore, which press outwards and therefore lock the working cylinder against the wall. However, this is not a particularly suitable solution, because the piston should slide in the cylinder bores and consequently the latter is lubricated.